This disclosure is generally directed to curable phase change inks, such as radiation-curable phase change inks, and their use in forming images, such as through inkjet printing. More specifically, this disclosure is directed to radiation-curable phase change inks, such as ultraviolet-light-curable phase change inks, that comprise a curable gellant and a crystalline polyester resin.
Inkjet printing systems are known in the art, and thus extensive description of such devices is not required herein. Phase change or “hot melt” inks are desirable for ink jet printers because they remain in a solid phase at room temperature during shipping, long term storage, and the like. In addition, the problems associated with nozzle clogging as a result of ink evaporation with liquid ink jet inks are largely eliminated, thereby improving the reliability of the ink jet printing. Further, in phase change ink jet printers wherein the ink droplets are applied directly onto the final recording substrate (for example, paper, plastic, cardboard, and the like), the droplets solidify quickly upon contact with the substrate, so that migration of ink along the printing medium is substantially prevented and dot quality is improved.
While phase change inks enable more facile image printing and printing onto porous substrates, these inks may exhibit microbanding. Microbanding is an uneven distribution of ink in an image area in which the image should be smooth and uniform. Because the ink temperature drops after ejection, the ink freezes (or gels) quickly upon contact with the substrate and an uneven distribution of ink on the image substrate may occur. The human eye can sometimes observe the uneven distribution as bands or lines in the direction of the substrate travel past the print head.
Microbanding may be addressed by leveling the ink on the image substrate by contact leveling. As used herein, the phrase “contact leveling” is a processing technique that employs a contact member, such as a roller, belt, press, wiper, to provide a sufficient amount of pressure to the ink surface in an effort to normalize or smooth the ink distribution. A heating element may be located near or within the contact member to heat it and consequently soften the ink for the leveling operation. Examples of contact leveling techniques include those described in U.S. Patent Application Pub. No. 2010/0103235, U.S. Patent Application Pub. No. 2010/0101716 and U.S. Patent Application Pub. No. 2010/0101717, each of which is incorporated by reference in their entirety. Additional examples of contact level techniques and apparatuses included those described in U.S. patent application Ser. No. 12/544,031, U.S. patent application Ser. No. 12/625,472 and U.S. patent application Ser. No. 12/814,741, incorporated herein by reference in their entirety.
However, contact leveling the phase change ink is also subject to issues. For example, contact leveling the ink via contact member may cause the ink layer to split. A portion of the phase change ink may thus be transferred to the contact member and affect the print quality of later processed images. For example, a portion of the ink transferred from a contact member may later be deposited on subsequent media contacted by the contact member to leave a ghost of the previously leveled image. Further, ink build up on a contact member necessitates either replacement of the contact member or removal of the ink from the contact member on a periodic basis. Consequently, addressing the microbanding defect of a phase change ink in an image without splitting the ink or accumulating ink on a contact member would be useful. While use of a release fluid in the contact leveling procedure may reduce ink splitting and transfer, elimination of the use of release fluids by design of inks that are less prone to splitting and offset may also be useful.